Rich Felker suggested removing dprintf() from watch, and one thing led to

another... This adds bb_xspawn() support, which does vfork/exec.  (I don't
know why using a static instead of a local adds ~40 bytes, but using
the local doesn't work...)

coreutils/watch.c

@@ -4,20 +4,7 @@
  *
  * Copyright (C) 2001 by Michael Habermann <mhabermann@gmx.de>
  *
- * This program is free software; you can redistribute it and/or modify
+ * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- * General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
- *
  */
 
 /* BB_AUDIT SUSv3 N/A */
@@ -41,23 +28,18 @@
 
 int watch_main(int argc, char **argv)
 {
-	const int header_len = 40;
+	int width, len;
-	time_t t;
-	pid_t pid;
 	unsigned period = 2;
-	int old_stdout;
+	char **watched_argv, *header;
-	int len, len2;
-	char **watched_argv;
-	char header[header_len + 1];
 
-	if (argc < 2) {
+	if (argc < 2) bb_show_usage();
-		bb_show_usage();
+
-	}
+	get_terminal_width_height(1, &width, 0);
+	header = xzalloc(width--);
 
 	/* don't use getopt, because it permutes the arguments */
 	++argv;
-	if ((argc > 3) && !strcmp(*argv, "-n")
+	if ((argc > 3) && !strcmp(*argv, "-n")) {
-	) {
 		period = bb_xgetularg10_bnd(argv[1], 1, UINT_MAX);
 		argv += 2;
 	}
@@ -65,44 +47,22 @@ int watch_main(int argc, char **argv)
 
 	/* create header */
 
-	len = snprintf(header, header_len, "Every %ds:", period);
+	len = snprintf(header, width, "Every %ds:", period);
-	/* Don't bother checking for len < 0, as it should never happen.
+	while (*argv && len<width)
-	 * But, just to be prepared... */
+		snprintf(header+len, width-len, " %s", *(argv++));
-	assert(len >= 0);
-	do {
-		len2 = strlen(*argv);
-		if (len + len2 >= header_len-1) {
-			break;
-		}
-		header[len] = ' ';
-		memcpy(header+len+1, *argv, len2);
-		len += len2+1;
-	} while (*++argv);
-
-	header[len] = 0;
-
-	/* thanks to lye, who showed me how to redirect stdin/stdout */
-	old_stdout = dup(STDOUT_FILENO);
 
 	while (1) {
-		time(&t);
+		char *thyme;
-		/* Use dprintf to avoid fflush()ing stdout. */
+		time_t t;
-		if (dprintf(1, "\033[H\033[J%-*s%s\n", header_len, header, ctime(&t)) < 0) {
-			bb_perror_msg_and_die("printf");
-		}
 
-		pid = vfork();	/* vfork, because of ucLinux */
+		time(&t);
-		if (pid > 0) {
+		thyme = ctime(&t);
-			//parent
+		len = strlen(thyme);
-			wait(0);
+		if (len < width) header[width-len] = 0;
-			sleep(period);
+		
-		} else if (0 == pid) {
+		printf("\033[H\033[J%s %s\n", header, thyme);
-			//child
+
-			dup2(old_stdout, STDOUT_FILENO);
+		waitpid(bb_xspawn(watched_argv),0,0);
-			execvp(*watched_argv, watched_argv);
+		sleep(period);
-			bb_perror_msg_and_die("%s", *watched_argv);
-		} else {
-			bb_perror_msg_and_die("vfork");
-		}
 	}
 }

include/libbb.h

@@ -146,6 +146,8 @@ extern void  bb_fflush_stdout_and_exit(int retval) ATTRIBUTE_NORETURN;
 
 extern void xstat(const char *filename, struct stat *buf);
 extern int  bb_xsocket(int domain, int type, int protocol);
+extern pid_t bb_spawn(char **argv);
+extern pid_t bb_xspawn(char **argv);
 extern void bb_xdaemon(int nochdir, int noclose);
 extern void bb_xbind(int sockfd, struct sockaddr *my_addr, socklen_t addrlen);
 extern void bb_xlisten(int s, int backlog);

libbb/xfuncs.c

@@ -182,3 +182,37 @@ void bb_xfflush_stdout(void)
 	}
 }
 #endif
+
+#ifdef L_spawn
+// This does a fork/exec in one call, using vfork().
+pid_t bb_spawn(char **argv)
+{
+	static int failed;
+	pid_t pid;
+
+	// Be nice to nommu machines.
+	failed = 0;
+	pid = vfork();
+	if (pid < 0) return pid;
+	if (!pid) {
+		execvp(*argv, argv);
+
+		// We're sharing a stack with blocked parent, let parent know we failed
+		// and then exit to unblock parent (but don't run atexit() stuff, which
+		// would screw up parent.)
+
+		failed = -1;
+		_exit(0);
+	}
+	return failed ? failed : pid;
+}
+#endif
+
+#ifdef L_xspawn
+pid_t bb_xspawn(char **argv)
+{
+	pid_t pid = bb_spawn(argv);
+	if (pid < 0) bb_perror_msg_and_die("%s", *argv);
+	return pid;
+}
+#endif